Visitor quote: "I thought I'd be hearing just another "six + one",
the world's most common and boring speakers. Hmm...These speakers makes you
forget about the 100 litre bass cabs missing".

Good fortune brought me in touch with the producer of the ribbon tweeter
seen below and after thorough testing, I set up a two-way from a new AudioTechnology 18H52 driver fitted with
a new titanium voice coil former, thus two
new drivers.
I've used ribbon tweeters before but never felt I had to go
back, but this ribbon changed my feelings. Being a fairly large ribbon,
it displays an impressive frequency response and very low distortion all
the way down to 1 kHz, allowing a wider range of crossover options than
usual, thus a 2nd order filter at 2 kHz is possible.

The "thing" about this ribbon tweeter is that the gaps between the ribbon
and poles of magnets are sealed with a U-shaped mylar suspension,
thus reducing air turbulence, increasing sensitivity and reducing
distortion. And it works! This ribbon tweeter delivers some of the best
highs I've had, regardless of brand, principle and price. The naturalness of cymbals, violins,
whatever is astonishing. Put the best money can buy in front of it - and
it delivers.
Now, no tweeter can do it alone. We need a seriously good mating partner, thus -

Per Skaaning at AudioTechnology made me a pair of 18H52 mid-woofers
featuring titanium voice coil formers. The result is a driver with an
exceptional linear response, in fact ruler flat up to 5 kHz with a small
notch at 6 kHz after which the response rolls off smoothly. Easy on
crossover - if baffle allows. The actual baffle is what can ruin a nice
infinite baffle response, thus several baffles and driver positions were
tried before I settled on what can be seen below. This will always be a
compromise because we have constraints on baffle design. We could
probably come up with an even better front panel - and nobody would
build it. And just having the best intrinsic frequency response doesn't
necessarily guarantee better sound. All depends!
For the ATS4-HE I used a passive radiator with the midrange. Works very
well, and here we take full advantage of the PR units rather than the
usual port. Admitted, this PR unit is many times the cost of a plastic
port and should you want to cut cost, you can use a 68 mm port instead.
Cut it to 18 cm length. Using the PR unit delivers a solid, potent bass for the size of the midbass.
Don't expect earthquake scenarios from a 6" driver, although bass does
remarkably well. This driver is fast, clean and has dynamic headroom in
abundance to put it short.

I may have failed in staying cool and calm in describing the drivers
presented here, but so be it. Yes, I'm freaking nuts about this small
speaker, having given me a new dimension to my record collection and
pointing to future projects. This is all I ask. Having built more than
200 speakers over the years, I need drivers that give me new
experiences
and point to new directions.
Visitors can't believe the bass these speakers can deliver, the clarity
of the midrange - even at high SPLs - and the uncoloured treble. We
listen to dubious tracks we usually skip, because they simply don't
sound bad any more. We discover details previously hidden and musical
layers being freed of congestion. Clarity!

The crossover follows an LR2 topology with a point of crossover around
2200 Hz. Having a tweeter sensitivity around 98 dB obviously takes some
attenuation to align the tweeter with the midbass around 87 dB, thus
R1-4.
For the midbass R7/L3/C3 dampens the 6 kHz peak. During crossover
development this peak was unattended as it is so low it doesn't
compromise treble performance, but it turned out that the LCR circuit
improved phase tracking in all of the crossover region and
significantly improved sound, so it stays
in place.

Ad squares and rectangles to your brace and distribute holes like seen
here.

Click image to view large

The tweeter front panel must have the dimensions shown on drawing to the
left. What's behind the tweeter is fully up to you.
To the right a suggestion to add more visual weight to the tweeter
housing. Tweeter side panels must be chamfered 45° not to impact
tweeter frequency response. The tweeter front panel must be 12 mm behind
mid-bass front panel.

Everything starts with building prototypes and testing different
crossovers under normal living room conditions.
From simulation it's easy to set up different crossovers that basically
deliver the same tonal balance, yet sound quite different.
In addition to this, four different amplifiers, solid state as well as
tube amps, are used for digital and vinyl playback.
The speakers here run very well from my 32 wpc
EAR-861 power amplifier.

Workshop images

What a thrill making small cabs! No huge, chunky bass cabs to move
around...

Front panel made from 30 mm laminated BB with mahogany fillets. Takes
some time, but I love the look of it.

PR unit seen from inside and rear.

Routing for the 18H driver. DO NOT forget to chamfer driver holes! This
driver needs air to breathe.
With laminated front panels like these I add one coat of lacquer before
routing to reduce edge ripping.
Start with 0.1-0.2 mm at a time and move router slowly!

Bitumen pads in place. 0.5 sqm supplied with kit.

Felt in place. For once, also cover front panel where possible.

Gluing front panels.

Ready for lacquer and first coat.

Parts for tweeter housing ready. To the right gluing tweeter cabs. Takes
quite a few clamps!

Place crossover at bottom of cabinet and fold a piece of acoustilux to
cover.

Damping behind 18H52 driver. One piece of acoustilux is covering the
bracing frame and up on the top of cabinet.
Cabinet here seen from top.

A few comments on MEASUREMENTS before you
start interpreting all the readings below.First of all, if we think measurements will
tell us how a speaker sounds, we're wrong. The perception of sound is
way too subjective to be reflected in any measurements we can perform. A
loudspeaker system is meant to give us a satisfying idea of an acoustic
event and for some people a pair of 5 USD ear-plugs are enough, others
spend 200 kUSD on a truly full-range pair of speakers - and the latter
may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too
much or too little energy in certain areas, although dispersion
characteristics play a vital role here. A two-way 7+1 and a three-way
7+4+1 may display similar horizontal dispersion, yet sound very
different. Measurements may tell us about bass extension if far-field
measurements are merged with near-field measurements. In addition to
this, ports may contribute to bass extension. Most of we diy'ers do not
have access to an anechoic room for full-range measurements from
20-20000 Hz.
What cannot be seen is what kind of bass performance we get in a given
room. Bass performance is highly dependent on in-room placement of your
speaker and the same speaker can be boomy in one place and lean in
another. Actual SPL level at 1 meter distance and 2.8V input is useful
for en estimate of system sensitivity and combined with the impedance
profile may give an idea of how powerful an amplifier is needed to drive
the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless
displaying serious linear distortion. The level of transparency, the
ability to resolve micro-details, the "speed" of the bass, etc., cannot
be derived from these data. Distortion measurements rarely tell much
unless seriously bad, and most modern drivers display low distortion
within their specified operating range.
Many people put way too much into these graphs and my comments here are
only meant as warning against over-interpretation. There are more to
good sound than what can be extracted from a few graphs. Every graph
needs interpretation in terms of what it means sonically and how it
impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the
speaker, because speaker cones made from polypropylene, aluminum,
Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even
diamonds all have their way of adding spices to the stew. Nor do
measurements tell what impact the quality of the crossover components
add to the sound, from state of the art components to the cheapest of
coils and caps, they all measure the same if values are correct, yet
sound very different.

GRT-145: More interestingly is the vertical dispersion, usually the weak
point of ribbons, but here we see a very good result.
Vertical dispersion at 0, 10, 20, 30 and 40 deg. off axis.

18H52-17-06-SDT frequency response on 65 x 100 cm baffle (green) and
actual speaker baffle (red).
On an infinite baffle we have a sensitivity around 90 dB/2.8V/1 meter.
On a narrower baffle we obviously have the inevitable baffle step loss,
thus around 87 dB sensitivity i all of the midrange.
What pleases me is the extreme linearity in the crossover region, here
all the way up to 5 kHz.

Should have fallen in love with Be domes - and I know a lot of people
think it's the holy grail - then this version. I have a lot of questions
regarding replacement of tweeters with Be domes, and normally not
possible without changes to the crossover. Implementing the ScanSpeak
D2908/714000 was easy as I already had a housing suitable for such
application. The ATS4-HE dome cabinet fits well on the top of the ATiRi
cabinet, so just follow the design and you're safe. For any of the
tweeters you can obviously make the cabinet completely to your liking as
long as you stick to the exact front panel dimensions and tweeter's
placement. It can be as simple as my test panels and it will work as
intended.